Tire size

[hsdady]

Hey guys long time no talk. Just got back in the country and is time for new shoes.

Currently I have T-Stars on my 850 with 235/45/17 front and 265/40/17 in the rear

I want to move to 245 front and 275 rear. What is the exact size that works best with the T-Stars? 245/40/17 and 275/40/17?

Please advise what size works best

[cartoonz]

245/45/17 front
275/40/17 rear

[kiwiCSi]

Yes, if you go up to 275 on the rears there are more choices.
Standard sizes of 235/45 and 265/40 are only available in a couple of brands, including Toyo Proxes.

https://www.bimmerforums.com/forum/s...-Tires-for-CSi

[hsdady]

Thanks gents. I went with 245/40/17 front and 275/40/17 rear. I found matching tires with BF Goodrich G-Force Comp 2 A/S and they ride pretty smooth as far I can tell. I also got an annoying "shimmy" fixed and maybe there is a learning coming from this. I used to have this shimmy between 60-80 and I knew it wasn't the rim or the suspension. The Discount tires monkey kept telling me the balance is perfect. Well the balance wasn't perfect by their rotating machines. When I swapped my tires to the BF Goodrich G-Force Comp 2 A/S the new tire shop done a road force balance before and the tire was bad, I mean really bad. No wonder I had the shimmy. O well. Moral of the story is do a road force balance with the right Hunter (http://www.hunter.com/wheel-balancers) equipment and people who know what they're doing. Discount tire kids kept telling me they also do road force balance but they use their own technology and equipment brand. Is total BS, they don't do a true road force balance and they don't use the Hunter machines. Won't give my business to Discount Tire ever again.

Two quick follow up questions:

1. My PSI now is at 32. Is that about right for these tires?
2. For long time storage what do I need to do to avoid flat spots on my tires? Increase PSI or use some special equipment?

Thanks again for all valuable guidance

[cartoonz]

You Cannot use the same profile tires when mixing 245 & 275...

[hsdady]

Well I just did. What's the risk?

You Cannot use the same profile tires when mixing 245 & 275...

[cartoonz]

traction control will constantly argue with you, this is a common mistake.
You can use all sorts of different sized tires, but the circumference has to be the same all around, +/- a wee bit - and the difference here is well beyond that threshold.

245/40/17 and 274/40/17 has a 3.9% difference - will cause trouble
245/45/17 and 275/40/17 has a 0% difference
245/40/17 and 275/35/17 has a 0.4% difference and works fine

The car will quickly realize that the front wheels are turning an extra 31 revolutions / mile vs the rear tires and it will freak out trying to compensate for that.
This is the reason you had different profiles on your original setup and also why every answer you were given followed the same formula.

Honestly, instead of trying to bump the fronts up to 245/45, I'd be looking to bump the rears down to 275/35 at this point... the fronts get perilously close to things with that width and higher profile.

[bruinbro]

I might be wrong but the ABS might freak out also.

[hsdady]

Well crap, now I have to go back to the shop and swap them. Can I live with them or I really need to swap them? Is not my daily car. It actually drives very nice. Took it up to 145 and no ABS or traction control warnings? Thanks much

[bruinbro]

Sure your TC and ABS systems are working?

[hsdady]

Never mind, I am an absolute idiot. After all looking at my car I do have 245/45/17 in the front. For some reason I thought they put 245/40/17. Looks like my tire guy is smarter after all :-) Thanks all for your feedback and concerns and that explains why the ABS and TC systems are working fine.

So next to the 2 questions:

1. My PSI now is at 32. Is that about right for these tires?
2. For long time storage what do I need to do to avoid flat spots on my tires? Increase PSI or use some special equipment?

[bruinbro]

Put the car on jacks or some sort of lift.

[Chillax]

Just a kindly FYI, the tire fitment calculator (excel spread sheet) is located here:->>
http://www.bmwccae31.com/info-how-tos/

[hsdady]

Many thanks. Lots of manuals and instructions there. I am sure my indy mechanic could use some of these

Just a kindly FYI, the tire fitment calculator (excel spread sheet) is located here:->>
http://www.bmwccae31.com/info-how-tos/